X-ray tube with means to selectively deflect the electron beam to plural targets



Nov. 24, 1964 5 P. STANHOPE 3,158,745

X-RAY TUBE WITl-i MEANS TO SELECTIVELY DEF'LECT THE ELECTRON BEAM TOPLURAL. TARGETS Filed Aug. 14, 1962 INVENTOR GORDON P. STANHOPE vat 63ATTORNEY United States Patent X-RAY TUBE WHTH l fEANS T0 SELdCTlt ELYEE- TE ELECEGN BEAM T0 PLURAL TARGET S Gordon l. dtanhope, Eerea, Qhio,assignor to General Electric Company, a corporation of New York Filed14, 1962, Ser. No. 216,794 1 illaim. (1. 250-9?) Tlcu's inventionrelates to X-ray tubes and more particularly, to an X-ray tube whereinthe emergent beam of X-radiation may exit the tube window directed inone of at least a plurality of alternative angles or patterns.

In the industrial application of X-radiography, it is sometimesdesirable to have the emergent X-ray beam extend over a full 360pattern. Such a panoramic pattern has application, for example, toinside-out radiography of a complete circumferential pipe weld which isaccomplished by inserting the X-ray tube output window within the pipeor pressure vessel itself in the region of the weld. This provides acomplete circumferential radiograph of the weld with a single exposure.In other industrial applications, it is necessary, on the other hand, toutilize a conical X-ray beam for radiographic purposes, as in inspectionfor flaws of cast ngs, aircraft assemblies and the like. Both theseindustrial applications may require similar energy levels; thus, forboth the 360 circumferential beam and for the conical beam, a usefulenergy level may be in the range of 100 to 500 kilovoltspeak. However,it has heretofore been necessary to have two separate and differentX-ray tubes when both insideout radiography and conical beam radiographywere required.

It is accordingly an important object of this invention to provide animproved Xray tube capable of providing a plurality of emergentX-radiation patterns.

It is another object of this invention to provide an improved X-ray tubecapable of providing both a 360 X-ray beam and a conical X-ray beam asrequired.

The major advantage of the X-ray tube in accordance with the inventionis that a single X-ray tube may be utilized for an entire range ofindustrial applications. Thus, both inside-out radiography ofcircumferential pipe welds as well as examination by conical beam ofcastings and the like, may be accomplished by a single tube.

In accordance with the principles of the invention, the above objectsand advantages are provided by an X-ray tube with a special target anodehaving a plurality of flat target faces disposed at an angle to eachother, in combination with means for causing the electron beam toimpinge upon any one of the target faces dependent upon which radiationangle or pattern is required at the time. The electron beam isdeflectable between the plurality of target anode surfaces whereby theemergent X-radiation from one anode surface is at an angle or has apattern, different from the emergent X-radiation from a second surfaceby virtue of the d lference in the angular orientations of the twosurfaces.

In a preferred embodiment of the invention to be discussed in detailbelow, one angular orientation of one target anode surface isperpendicular to the electron beam, whereupon the emergent X-radiationis disposed in a circumferentially complete 360 radiation pattern, whilethe second target anode surface is disposed at an obtuse angle to theelectron beam to thereby provide a conical radiation pattern.

In another application of X-radiation, analysis of materials by X-rayabsorption analysis is provided. In such an arrangement, X-rays arepassed through a test specimen and then applied to the diffractioncrystal, the output of which provides the information for identifyingthe composition of the test specimen. Such an arrangement 3,158,745Patented Nov. 24, 1964 is especially practical when trying to ascertainwhether a specific substance is contained within the test specimen.Since the type of target anode material determines in substantialmeasure the Wavelength of the output X-ray beam, it is understandablethat different target materials are appropriate for specimens havingdifferent constituents, to provide the most efficient or effectiveexamination. For this reason, it is desirable to be able to provide anoutput X-ray beam from the tube which may be derived from a plurality ofseparate target anode materials.

In the instance of X-ray emission analysis as for quantitative analysisof an element or contaminant in a specimen, the X-ray wavelengthrequired is one which is at an energy level only slightly in excess ofthat required for exciting characteristic radiation from that element.Too high an energy level may result in non-linear and unpredictablyinterdependent background radiations scattered by the sample which wouldmask the measurement of the element of interest, or would have to bediscriminated against to obtain the proper measurement. Where more thanone element is under analysis, having spaced characteristic radiationwavelengths, it follows that more than one target material is calledfor. Use of a plurality of target materials desirably eliminates theneed for filters in the primary or secondary beams, since filters oftenresult in a serious reduction of the intensity of the desired radiation.

A further use of X-radiation is in the study of the diffractioncharacteristics of a specimen material when irradiated with particularand known wavelengths of X-radiation. The diffraction characteristics ofthe specimen will vary and be dependent upon the incident radiationwavelength, and it is, therefore, important to have easily controlledand readily available sources of X-radiation with dfering characteristicwavelengths.

It is another object of this invention, therefore, to provide animproved X-ray tube having an output beam for use in diifraction,emission or absorption analysis which may be derived from one of anavailable plurality of different metallic target anode materials.

This object is accomplished in accordance with the principles of theinvention by providing a target anode having a plurality of surfaces,each consisting of a different metallic material and deflecting theelectron beam of the X-ray tube to the desired one of the plurality ofangularly related target anode surfaces.

The novel features believed to be characteristic of this invention areset forth with particularity in the appended claims. The inventionitself, however, both as to its organization and method of operation,together With fur ther objects and advantages thereof, may best beunderstood by reference to the following description taken in connectionwith the accompanying drawings.

In the drawings:

FIGS. 1 and 1A are cross-sectional and schematic views of an X-ray tubein accordance with the principles of the invention, utilizingelectrostatic electron beam deflection;

FIGS. 2A and 2B are views of the anode construction of the tube of FIGS.1 and 1A under difierent operating conditions;

FIG. 3 is an alternative tube construction to that of FIGS. 1 and 1A;and

FIGS. 4 and 5 are alternative anode constructions to those of FIGS. 1through 3.

In FIGS. 1 ad 1A, there is shown an end-grounded X-ray tube 29,constructed in accordance with the present invention. It comprisescathode 21 to generate a stream of electrons which are guided andcontrolled by consecutive control electrodes 22, individually identifiedas 22a, 22b and 22c, to form a beam, indicated generally by axis line23, which impinges upon one of the two target plate surfaces 24a or 24!)supported on the faces direction of axial path 23 to be taken by thehigh voltage electron beam moving from cathode 21 to target anode 25.In'this embodiment the accelerating potential is preferably 300 k.v.p.Intermediate connections from transformer winding 28 are made to controlelectrodes 22a, 22b and 220, to establish the fields to help guide andshape the electron beam in its passage between cathode 21 and anode 25.T o be properly eflective, control electrodes 22 should be in coaxialalignment with each other and with common axis 23. A three-point supportis provided for each control electrode 22 to provide a relatively stablesupporting system to maintain the coaxial disposition of the electrodes.

The ultimate support for control electrodes 22 is derived from a unitarydielectric column, as a tube or cylin der 35, of glass or ceramic.Cylindrical column 35 supports the control electrodes 22, and alsoconfines and encloses them in an evacuated chamber or region 37 withincylinder 35. This chamber 37 is hermetically sealed to maintain a highvacuum. Glass column 35 is supported at its opposite ends on thesupporting structures associated with cathode 21 and anode 25,respectively. The connections betweenthe column and those supportingstructures are made as hermetic seals, in order to maintain the desiredvacuum within'the imitary glass column 35. The details of thosesupporting and sealing connections are considered in detail in. theUnited States Patent No. 3,034,009, of M. J. Zunick et al., entitled PinSeal Accelerator Tubes.

With'the exception of deflecting electrodes 51 and target anode 25, theX-ray tube of FIGS-'1 and 1A is a conventional X-r ay'tube of the typedisclosed in detail, for example, inthe United States Patent No.2,853,622 of C. W. Hansen, entitled Electron Discharge Apparatus,utilizing the unitary dielectric support envelope and mounting devicesof the above mentioned United States Patent No. 3,034,009.

The target plates 24a and 2412 are embedded in the faces 54a and 54b oftarget anode 25. The bulk of' anode is of copper, while target plates24a and 2415 are preferably of tungsten bonded in the copper. The faces54a and 54b of anode 25 are disposed such that surface 54a and plate 24aare perpendicular to the axis line 23 defining the path of the electronbeam when undeflected. Target plate 24a in surface 54:: is positionedsuch that 'theelectr'on beam impinges upon plate 24a when the electronbeam is not deflected. The target surface 54b and plate 24b aredisposed, in this embodiment, at an angle of 22.5 from the plane definedby surface 54a. When, under the influence of the deflectingelectrodes51, the electron beam is deflected, it impinges upon target plate 24b insurface 54b. v

Circumscribing anode 25 in the region of target plates 24a and 24b isthat portion of the X ray tube forming the output window 55. Window 55is a thin walled cylinder of beryllium oxide having a Wall thickness ofapproximately 100 mils. Window 55 is therefore effectively transparentto X-radiation. The electron beam that may impinge upon the tungstentarget plate 24:: under the influence of the 300 k.v.p. acceleratingpotential, provides an output X-radiation pattern in the plane of anodesurface 54a of 360 and in the plane perpendicular to that and relativeto surface 54a, as shown in .FIG. 2A. 1

Since the beryllium oxide window is in the cylindrical 4. formdescribed, the entire radiation pattern emerges from the tubeundisturbed and illuminates the circumferential weld 57 of pipe 53 underinspection.

When the electron beam'impinges upon target plate 24b in surface 5412,as shown in FIG. 23, however, the output beam provides the usual conicalradiation pattern. The angle of the cone in the arrangement shown is 45with surface 54b defining one side of the angle. Anode 25 is a coppercylinder with a section removed to form surface 54b as by a planecutting through that end section of the cylinder at an angle of 225 toend surface 54a.

Deflecting electrodes 51 may be energized by a tap off the secondary oftransformer 27 as shown in FIG. 1A, or by an auxiliary winding. One ofthe deflecting electrodes 51 is grounded wmle the other electrode mayeither be grounded, or switched to place it in circuit with that part ofthe secondary Winding providing the de-. flection potential throughsingle pole double throw switch' 64- or some other suitable electronicor solid state sWitch-.

ing device. With switch 64 positioned on'contact 65, electrodes 51 aregrounded; the deflecting electrodes are therefore inactive and the beamproceeds along axis line 23 to strike surface plate 24a of the targetanode 25. With switch 64- positioned on contact 66, the deflectionportion of the secondary winding is brought in circuit with the electro-es 5 1. The electron beam is thereby deflected along a path indicatedby line 73 to strike'the angled target surface 24b of target anode 25.

To insure that the electron beam impingement is restricted to the twotarget plate surfaces 24a and 24]; under the tube operation, thefollowing typical values may be assigned to the various parametersinvolved. With a distance L of ten inches between the center of thedeflecting electrodes 51 and anode surface 54a, a deflection distance Dof 0.2 of an inch represents the total deflection of the center of theelectron beam at its point of impingement at surface 24a and its pointof impingement on sur face 24b, with a distance a of 0.45 of an inchbetween the two deflecting electrodes 51, and with a deflection elecrodelength Z of 1.6 inches, a deflection voltage V applied to the electrodes51 of 3.7 k.v.p. is necessary, with an accelerating voltage V, of 300kyp. equation: I

defines the general relationship applicable to any tube.

With the electrostatic deflection derived from the tap off secondarywinding 28, the magnitude of deflection is always constant,.sincesynchronized deflection relative to the accelerating potential is alwaysobtained, Thus, be-

cause electrostatic deflection is always directly proportional to theratio of deflecting voltage and accelerating voltage, and because thesecondary voltages of the transformer are always in constant ratio andphase, i.e., V /V is constant, deflection is constant for any magnitudeof tube accelerating potential, both instantaneously and for variousl-:.v.p. values.

When an auxiliary winding is used with AC. operation in lieu of a tapoff the stack winding, the powersource for the deflecting coils must besynchronized with the main power supply and an appropriate amountofphase shift introduced Where necessary to insure proper synchronization.Deflection of the electron beam by electromagnetic means'rather than theelectrostatic system disclosed in- FIGS. 1 and 1A may, where thecircumstances so indicate, be appropriately utilized. Permanent magnetsmay also be mounted about the tube in the same region as, but in lieuof, the electrostatic deflecting electrodes, for the purpose ofproviding the required deflection. In such an arrangement it may bedesirable to use a DC. accelerating voltage for theX-ray tube ratherthanthe A.C. potential applied in FIGS. 1 and'lA; In FIG. 3, a targetanode construction is shown for use with deflection by permanent magnet.The axis line 23 intercepts the line of intersection of the angled andperpendicular faces 64b.

The general and 64m of target anode 65. With the permanent magnetoriented in a first position with the magnetic pole pieces as shown inFIG. 3, deflection of the electron beam is as indicated along line 74and impinges upon the target plate in surface deb. With the polarityreversed, that is, the permanent magnet rotated 180 about the tube, thebeam is deflected to the target plate of surface 6-la.

In PEG. 4, there is shown a target anode construction 85 wherein thereis no surface perpendicular to the electron beam; both surfaces areangled with the surfaces intersecting along a diametral line at the apexof the anode. In this construction, the X-ray beam emerges in a conicalradiation pattern from each of the target plates of surfaces 84a and84b. The permanent magnet type deflection is appropriate in such anarrangement, since rotation of the magnet by 180 results indirectswitching from target anode face 84a to target face 3%. In the case ofthe utilization of such a tube for X-ray diffraction or emissionanalysis, one of the target plate surfaces may be of a first material,such as tungsten, while the other target plate surface is of another,such as chromium. The accelerating voltage for an X-ray tube used indiffraction or emission analysis typically is continuously variable upto 75 l-:.v.p. and up to 100 milliamperes. Any appropriate combinationof materials may be utilized. A group of metals from which selection maybe made for most practical purposes is tungsten, chromium, molybdenum,copper, nickel, cobalt, iron and silver.

in FIG. 5 is shown another anode construction 95 wherein the anode ismulti-faced, whereby the top portion has a pyramidal type constructionwith each face of pyramid representing a different target surface. Eachsurface may support a different target plate material, preferably fromthe aforementioned group of metals. Deflection of the beam from one toanother of the pyramidal anode surfaces may readily be accomplished byrotation of the permanent magnet about the circumference of the tube atthe point of deflection. With the target anode construction of FIG. 5,the permanent magnet has three defined operational positions about thedeflection region of the tube, spaced 120 apart, to provide electronbeam deflection to each of the three surfaces.

While the principles of the invention have now been made clear inillustrative embodiments, there will be immediately obvious to thoseskilled in the art many modifications in structure, arrangement,proportions, the elements, materials, and components, used in thepractice of the invention, and otherwise, which are particularly adaptedfor specific environments and operating requirements,

without depmting from those principles. The appended claim is thereforeintended to cover and embrace any such modifications, within the limitsonly of the true spirit and scope of the invention.

What is claimed as new and desired to be secured by Letters Patent oftheUnited States is:

An X-ray tube comprising: an anode; a cathode; means for acceleratingthe electrons from said cathode in a beam to said anode; said anodehaving at least two distinct electron target surfaces defined by twoplanes 'mtersecting at an angle, one of said planes being disposedperpendicular to the longitudinal axis of said X-ray tube deflectingelectrodes disposed on either side of the path of said electron beambetween said cathode and said anode for deflecting said electron beambetween said two surfaces, means to selectively vary the direction ofthe deflection forces from said deflecting electrodes; an output X-raytube window substantially transparent to X-radiation and cylindrical inshape circumscribing said anode, said cylindrical window being coaxialwith the longitudinal axis of said X-ray tube; said electron acceleraing means comprising a plurality of accelerating electrodes tapped off aresonant transformer providing an accelerating voltage of magnitudesufficiently great to generate a circumferential beam of X-rays whensaid electron beam impinges upon said perpendicular target surface and aconical beam when said electron beam impinges upon other of said targetsurfaces, but insuficiently great to permit said electron beam and theX-rays generated thereby to pass through said anode and out of said tubeat any point other than through said cylindrical window.

References Cited by the Examiner UNlTED STATES PATENTS OTHER REFERENCESRoof-Top-Target Tubes, Electronics, by E. F. Weller, March 14, 1958, pp138-139.

RALPH G. NlLSON, Primary Examiner.

